This invention relates generally to microstrip antennas and microstrip antenna arrays and is particularly directed to microstrip antennas and arrays which have selectable radiation patterns at a single frequency. This invention also provides polarization diversity in these selectable mode microstrip antennas and arrays. This invention is also particularly directed to selectable mode antennas and arrays that are frequency-agile. The selectable mode, frequency-agility and polarization diversity is achieved in a single microstrip patch.
The microstrip antenna has been shown to be an excellent radiator for many applications requiring thin, inexpensive, conformal antennas which are rugged and have a low aerodynamic profile. However, many uses require a selectable radiation pattern. To achieve selectable mode capabilities in prior art antennas it was necessary to provide more than one microstrip patch, which was space and weight inefficient. For example, if it was desired to operate as a homing device and selectable mode capability was desired, it was necessary to provide alternate radiating patches of different dimensions.
For many applications, such as direction finding, fuzing, beam splitting, side lobe cancelling and low-gain beam steering, it is often highly desirable, especially when dealing with projectiles, missiles, aircraft and radar, to have single conductive patch microstrip antennas that have the capability of exhibiting selectable radiation patterns at a single frequency. It is also often highly desirable to have the capability of switching modes instantaneously, such as being computer controlled. The prior art single conductive patch microstrip antennas do not have the capability of selectable radiation patterns which can be switched rapidly and simply.
It is also highly desirable to have a selectable mode microstrip antenna or array that has selectable polarization diversity. To obtain polarization diversity in most prior art antennas it is necessary to have at least two antenna feeds and associated power dividers, phase shifters and rf switches to provide complete polarization coverage. For many applications it would be beneficial to obtain polarization diversity with simple inexpensive equipment that is easily controlled or that can be controlled by a digital computer.
Another highly desirable feature for many applications is to have a selectable mode microstrip antenna that is frequency-agile, as well as being polarization diverse. The prior art does not show single selectable mode microstrip antennas that have frequency-agility.
This invention provides a method to achieve selectable radiation patterns, frequency-agility and polarization diversity in both individual antenna elements and arrays and a method to achieve rapid selection of a radiation pattern, polarization, and frequency. The described method is inexpensive, easily constructed and easily controlled.
It is therefore one object of this invention to provide a microstrip antenna which is capable of selectively exhibiting selectable radiation patterns.
It is another object of this invention to provide a selectable mode microstrip antenna that is capable of providing selectable polarization.
It is a further object of this invention to provide a selectable mode microstrip antenna that is capable of providing frequency-agility.
It is still another object of this invention to provide a microstrip antenna that provides selectable radiation patterns, selectable polarization and selectable frequencies by means of simple electronic switching capable of being computer controlled, and thus instantaneously changeable.
It is still a further object of this invention to provide a microstrip antenna array that exhibits selectable radiation patterns, selectable polarization and selectable frequencies which are constructed by standard printed circuit techniques and are conformable and have low profile and desirable aerodynamic qualities.